Hello: Can someone help with this? A long, thin, nonconducting plastic rod is bent into a circular loop that has radius a. Between the ends of the rod a short gap of length l, where l << a remains. A positive test charge of magnitude Q is evenly distributed on the loop. What's the magnitude tof E at the center of the loop? I don't think we can use Gauss' law for this, because the rod is not connected? So does this mean that we should use dE = k*dq/r^2, and dq = ads, and ds = ad(theta) and integrate? But instead of theta being from 0 to 2*pi, we need to find the theta that is represented by the l, which is I guess l/a for very small theta. Also, I read in the book that the electric field is discontinuous at any location with an infinite volume charge density. Can someone explain that? How can there be an infinite volume charge density? Is it like when R goes to zero or something? Thanks.